I have a 71 and 72 bonneville. i have two front ends from yamaha 650's. the bearings are larger and the stem is longer on the yamaha, years ago I was told they were interchangable. Any tech or bearing numbers etc. would be appreciated. I want to change because of the disc brake as i want to ride the bikes more and i am in an area of heavy traffic. The conical (comical) front drum is just junk.
I do not have any experience with this particular swap, but I recently did mount a set of Cerianis on an OIF. I believe the only viable alternative is to fit a .75" diameter steering stem to the Yamaha trees. The problem is that the OIF steering head bearing "cup" has a unique outer diameter (BTW, the bearings are available at a typical auto shop - they are a common trailer wheel bearing) and there are no alternative inner "cone" bearings. HTH